1. Field of Invention
The present invention relates to a color filter and a method of manufacturing the color filter, and a solid-state image pickup element using the color filter.
2. Description of the Related Art
In recent years, as a manufacturing method of a color filter, a photolithography method has been used in consideration of production cost and ease of production.
This photolithography method refers to a method wherein a radiation-sensitive composition such as a colored curable composition or the like is applied on a substrate by a spin coater, a roll coater, or the like, and dried to form a coating film; the coating film is subjected to pattern exposure, development, and baking to form color pixels, and this cycle of operation is repeated for each color, thereby producing a color filter.
The photolithography method gives high positioning accuracy and has been widely used as a method suitable for manufacturing color filters for color displays of large screens and high-precision displays.
A known technique related to the photolithography method uses a negative photosensitive composition, in which is used a combination of an alkali-soluble resin with a photopolymerizable monomer and a photopolymerizable initiator (for example, see Japanese Patent Application Laid-Open (JP-A) Nos. 2-181704, 2-199403, 5-273411, and 7-140654).
Here, a general outline of the method of manufacturing the conventional color filter by the photolithography method is described with reference to FIGS. 32A to 36B.
As shown in FIGS. 32A and 32B, a colored negative curable composition is applied on a support 10 by means of a spin coater or the like to form a first color layer 42. After being prebaked, the first color layer is pattern exposed to light through a photomask 47 (i.e. a first color pixel-forming region 44 in the first color layer is exposed to ultraviolet radiation) as shown in FIGS. 33A and 33B. After that, an unnecessary region 46 in the first color layer is removed by development treatment, followed by post-baking treatment, thereby forming a first color pixel 48 as shown in FIGS. 34A and 34B.
Moreover, a second color pixel 50 as shown in FIGS. 35A and 35B and a third color pixel 52 as shown in FIGS. 36A and 36B are formed by repeating the same process as in the first color pixel formation, whereby a color filter is formed.
In the conventional manufacturing method of a color filter by the photolithography method, as shown in FIG. 36A, a problem occurs such that a region 54 where a color pixel is not formed is generated in the region where the corners of the color pixels gather. Moreover, there is also a problem in that a desired film thickness is not obtained in regard to each of color pixels. Furthermore, the film thickness of a region where color pixels contact mutually are not formed as intended (namely, a problem that a region 56 where the film thicknesses of the color pixels are thin is generated in the vicinity of the boundary of the color pixels as shown in FIG. 36B), and the like.
Although optimization of the mask bias or the like and improvements in the curing efficiency of a colored curable composition when exposed to a light source have been made, there is a limit to these improvements.
Moreover, although a technique is known which embeds the second color pixel or the like by thermal flow (reflow) at the time of thermosetting (for example, JP-A Nos. 2006-267352 and 2006-292842), this technique tends to be influenced by the performance and the process conditions of the colored curable composition to be used after the formation of the second color pixel, and there is, for example, a problem such that the heating distribution of a support will be reflected as it is in the embedding properties.
In addition, in a liquid crystal display device or a solid-state image pickup element, there have been advances in the reduction of pixel size, necessitating the reduction in size of a color filter. In particular, with the recent remarkable miniaturization of solid-state image pickup elements, a high resolving technology allowing resolution of less than 2.0 μm in size is needed, but a limit has almost been reached with respect to the resolution in the conventional photolithography method. For this reason, the issue of photolithography methods is becoming more and more prominent.
A technique using a dye has also been proposed as a technique for further miniaturization of a color filter and realization of a high-definition color filter for a solid-state image pickup.
However, a dye-containing curable composition is generally inferior to a pigment with respect to properties such as light resistance, thin film formation, or ease in change of spectral transmission characteristics. Further, since especially when manufacturing a color filter for use in the solid-state image pickup element, a film thickness of 1.0 μm or less is required, it is necessary to add a large amount of colorants in a curable composition, thereby causing various problems including significant difficulties in pattern formation, such as insufficient adhesion to a substrate, insufficient curability, or leakage of the dye in the exposed area.
Moreover, in contrast to the method of manufacturing the color filter using the photolithography method, a dry etching method has been known for many years as an effective method of forming a thinner film with a highly-fine pattern. The dry etching method has been conventionally utilized as a method of forming a substantially rectangular pattern.
Furthermore, a pattern formation method using a combination of the photolithography method and the dry etching method has also been proposed (see, for example, JP-A No. 2001-249218).
However, although the first color pixel may be formed into a rectangular form by the technique described in JP-A No. 2001-249218, formation of the second and third color pixels is rate-limited by the performance of the conventional photosensitive colored composition, and the problems accompanied with the photolithography method remain.
Therefore, when the photolithography method is used, it is necessary to increase the concentration of a colorant while maintaining the discrimination in dissolution properties between the compositions by exposure or development, and thus the technical hurdles are extremely high.
As described above, in the conventional method of manufacturing a color filter, there is a limit (lower limit) in the pattern size that can be formed.